Water Chemistry Variables Research Articles

Stream Water Chemistry in Mixed-Conifer Headwater Basins: Role of Water Sources, Seasonality, Watershed Characteristics, and Disturbances

Understanding the transport of dissolved organic carbon (DOC) and nitrogen (N) as water flows through headwater basins is important for predicting downstream water quality. With increased recognition of climatic impact on nutrient transport, more studies are needed in headwater basins experiencing a Mediterranean-type climate, such as those of the Sierra Nevada, California. We analyzed water samples collected over 5 years from eight low-order and mixed-conifer watersheds to elucidate the temporal variation of water chemistry and evaluate their responses to prolonged drought and low-intensity forest thinning. We observed higher stream DOC concentrations in October compared to other months within water years prior to drought and thinning, suggesting the importance of antecedent moisture conditions on seasonal C export. In unthinned watersheds, stream DOC concentrations were lower (62%) and DOC aromaticity was higher (68 and 92%, depending on the index used) during drought compared to non-drought years. In thinned watersheds during drought years, stream water had higher DOC concentrations (66–94% in three consecutive years following thinning) and dissolved inorganic N (24%, in the third year following thinning) compared to unthinned watersheds during drought. Additionally, lower stream DOC concentrations were found in watersheds with higher elevations and lower drainage densities in the year with near-average precipitation; however, these correlations were not significant in years with greater or extremely low precipitation. Taken together, our results suggest that stream concentrations of DOC and dissolved N in Mediterranean headwater basins are extremely variable over time due to the high temporal climatic variabilities and periodic management practices.

Dissolution of Different Reservoir Rocks by Organic Acids in Laboratory Simulations: Implications for the Effect of Alteration on Deep Reservoirs

Organic acids are important agents in the alteration of deep reservoirs. It is difficult, however, to assess the impact of organic acid alteration on deep reservoirs because different dissolution processes may occur during diagenesis. This study simulated the dissolution of three different types of reservoir rocks by acetic acid in a closed system and compared the mineral and elemental composition, surface morphology, pore structure, and water chemistry variations of the initial and altered samples. The study demonstrated that both micrite and sucrosic dolostone are strongly dissolved, losing about 20%–30% of their initial rock sample weights. Observation under SEM showed that the limestone dissolved homogenously, whereas the dolostone showed honeycomb-like dissolution. Both carbonate samples showed the development of large voids, including holes and cavities of micrometer scale, but nanopores of various sizes were blocked. In contrast, lithic arkose was heterogeneously altered, losing a weight proportion of about 13% by dissolution of calcite cement. These micrometer-scale microfissures were developed, but those nanometer-scale pores just varied in a narrow range of sizes. The volume increase in all three reservoir types is mainly attributed to the dissolution of carbonate minerals. In deep reservoirs, in situ generated organic acids can enlarge existing cavities in carbonates and develop microfissures in sandstones. The microfissure porosity in sandstone is limited but can increase through other geological processes such as overpressure. More importantly, these acids can maintain the acidity of pore waters, inhibit the precipitation of dissolved minerals, and help to preserve reservoir porosity. Although temperature plays an insignificant role in laboratory simulations, it influences both the generation and destruction processes of organic acids in deep reservoirs on geologic time scales and, thus, warrants further attention. The results provide a basis for recognizing the typical patterns of organic acid dissolution on different reservoir rocks and further suggest the potential role of organic acids in the formation and preservation of secondary porosity in deeply buried reservoirs.

Long-Term Interannual and Seasonal Links between the Nutrient Regime, Sestonic Chlorophyll and Dominant Bluegreen Algae under the Varying Intensity of Monsoon Precipitation in a Drinking Water Reservoir.

Long-term variations in reservoir water chemistry could provide essential data in making sustainable water quality management decisions. Here, we analyzed the spatiotemporal variabilities of nutrients, sestonic chlorophyll-a (CHL-a), nutrient enrichment, dominant algal species, and overall chemical water health of the third-largest drinking water reservoir in South Korea during 2000–2020. Our results distinctly explained the strong influence of monsoon rainfall on spatial and annual water chemistry variations. We observed a consistent increase in the chemical oxygen demand alluding to organic matter pollutants, while a steady declining trend in the sestonic CHL-a. The long-term total phosphorus (TP) level showed a steady reduction from the riverine zone to the lacustrine area. However, a higher total coliform bacteria (TCB) was observed at the water intake tower sites. TP displayed a strong link to algal CHL-a and ambient nitrogen phosphorus ratios, suggesting a robust phosphorus-limitation state. The severe phosphorus-limitation was also corroborated by the findings of trophic state index deviation. The high and low flow dynamics exhibited the strong influence of intensive rainfall carrying many nutrients and sediments and flushing out the sestonic CHL-a. Successive eutrophic conditions prevailed along with dominating blue-green algae species (Microcystis and Anabaena). We observed a strong positive correlation (r = 0.62) between water temperature and CHL-a and between total suspended solids and TP (r = 0.65). The multi-metric water pollution index characterized the overall water quality as ‘good’ at all the study sites. In conclusion, the long-term spatiotemporal variabilities of the ecological functions based on the nutrient-CHL-a empirical models are regulated mainly by the intensive monsoon precipitation. The drinking water could become hazardous under the recurrent eutrophication events and chemical degradations due to uncontrolled and untreated inflow of sewage and wastewater treatment plant effluents. Therefore, we strongly advocate stringent criteria to mitigate phosphorus and organic pollutant influx for sustainable management of Daecheong Reservoir.

Effects of environmental variables on littoral macroinvertebrate community assemblages in subtropical reservoirs

ABSTRACT Anthropogenic pressures on standing waterbody systems potentially result in changes to sediment and water qualities, and thus ecological community characteristics. We tested effects of drawdown on physical, water and sediment variables, as well as their effects on littoral macroinvertebrate community composition in two subtropical reservoirs. Water levels differed significantly between reservoirs and over time, with significant effects on several water chemistry parameters (e.g., pH, conductivity, Mg, Fe), whilst sediment properties were less affected. Significant effects of water level, site and macrophyte cover on macroinvertebrate community structures were not detected, however macroinvertebrate community structuring differed significantly over time. Redundancy analysis (RDA) highlighted that the first and second axes accounted for 45.6% of the total macroinvertebrate community and environmental variables relationship variance. Most of the sediment variables, such as Cu, Mg, Na and Pb and water chemistry (i.e., HCO3-), were positively associated with the first axis, while water temperature and pH were negatively associated with the first axis. The RDA variation partitioning showed that water and sediment chemistry variables accounted for 40.3% and 30.3%, respectively, of the total macroinvertebrate variation. The present study contributes to understandings of the interplays between water level, physico-chemical properties and community compositions in human-altered aquatic ecosystems.

Effects of a chain of reservoirs on temporal and spatial variation in water chemistry within an endorheic basin

Reservoirs provide more than 90% of water for agricultural, municipal, and environmental flows in arid regions. Yet, these resources may be compromised if the effects of reservoirs on water chemistry are not considered. This manuscript summarizes water chemistry data collected from May 2014 to October 2018 in the Shiyang Basin, an endorheic basin in arid North-Central China, where samples were collected from a chain of reservoirs, including headwater (mountain), mid-reach (oasis), and lower (desert) reservoirs. All samples consisted of a mixture of Ca-HCO3, Ca (Mg)-HCO3, and Na-SO4(Cl), with concentrations increasing at lower elevations. Stable isotopes indicate that most evaporation occurs in reservoirs, rather than in stream channels. Rock lithology is the primary factor influencing water chemistry in the headwater and mid-reach reservoirs, with the additional influence of imported water from the Yellow River in the mid-reach reservoir. Water quality in the desert reservoir was primarily influenced by evaporative crystallization. We show that these reservoirs are the primary source of hydrochemical transformation in this endorheic basin, affecting both the temporal and spatial variation of water chemistry.

Cyclic variations of quality characteristics in river water in an industrial region.

River water in industrial regions is a dynamic medium defined by random variables that cannot be described by linear equations. However, some water quality characteristics, e.g., pollutant concentrations, which look chaotically distributed are largely governed by deterministic laws resulting in periodic variations of water chemistry. Understanding this process will enable the researchers to analyse the history of the characteristics involved and to predict their future values. We provide further evidence of predictable, cyclic concentration behavior from the Iset River flowing through a heavily industrialized area in the Ob River basin, Ural Federal District, Russia. In particular, we found that the concentration of copper and nitrate can be characterized by pronounced fractals and quasi-cycles with predominant lengths of 7-8 and 4-5 months, respectively. Our results can improve forecast reliability and water use efficiency. Results from the Iset River could be potentially applicable to virtually any other river in the world, at least in temperate climate areas.

Abundance of an invasive bivalve, Corbicula fluminea, is negatively related to growth of freshwater mussels in the wild

Abstract Causes of worldwide freshwater mussel declines are poorly understood, and the potential role of the invasive Asian Clam, Corbicula fluminea, has received little attention. We measured survival and growth of captively‐reared juveniles of four native mussel species during 84‐day in situ exposures at 17 sites in the Rockcastle River system, Kentucky, U.S.A., where mussel declines are attributed to coal mining. We measured water temperature, a comprehensive array of water chemistry variables, and Corbicula abundance at each site during mussel exposures. Mussel survival was high (mean = 85.4%), did not differ among species, and was not related to any measured factor. In contrast, growth varied among sites by an order of magnitude, but growth responses were nearly identical for all four species. We found little evidence of water pollution from coal mining or other sources, and pollution did not explain variation in mussel growth. Growth was best explained by a model including only temperature (positive effect) and Corbicula abundance (negative effect) without interaction. Our model predicts 46% lower mass gain over 84 days for every 10‐fold increase in Corbicula abundance regardless of temperature, but growth may be reduced to unsustainably low levels in cooler streams. Previous ideas about water pollution as a cause of low growth and mussel declines were not supported by our data. Instead, the predicted strong effects of Corbicula, combined with similar responses of four mussel species, suggest that Corbicula may be an important, but overlooked, factor in widespread mussel declines.

Impact of salinity and carbonate saturation on stable Sr isotopes (δ88/86Sr) in a lagoon-estuarine system

Local carbonate cycling in lagoon-estuarine systems, involving processes such as inorganic and biogenic carbonate precipitation/dissolution, represents an important but poorly constrained component of the coastal carbon budget. This study investigates the sensitivity of stable Sr isotope tracer (δ88/86Sr) with respect to carbonate saturation and salinity of local waters in the Coorong, Lower Lakes and Murray Mouth (CLLMM) estuary in South Australia. The CLLMM has an extensive range of salinity from fresh to hypersaline (from ∼0 to over 100 PSU), with corresponding variations in water chemistry and major ion composition that in turn controls mineral saturation states, and thus CaCO3 precipitation/dissolution in local waters. Here we use the novel δ88/86Sr tracer in tandem with the more established radiogenic Sr isotope ratio (87Sr/86Sr), where the latter is a robust proxy for Sr sources and thus water provenance. We also produced a geochemical (PHREEQC) model of calcium carbonate (CaCO3) saturation changes across this unique lagoon-estuarine system.The results indicate a systematically increasing trend of δ88/86Sr (from ∼0.25‰ to ∼0.45‰) with increasing salinity and CaCO3 (aragonite, calcite) saturation indices of the coastal waters, which in turn suggest an overall control of carbonate dissolution/precipitation processes on the stable Sr isotope composition in the CLLMM system. This was further corroborated by Ca isotope data (δ44/40Ca) published previously on the same samples from the Coorong, as well as a quantitative simulation of local carbonate removal in the lagoon based on Rayleigh modelling and Sr isotope data.Overall, our results confirm that a coupled Sr isotope approach (combining 87Sr/86Sr and δ88/86Sr) can be used to constrain not only the main water sources (continental versus marine Sr) but also local CaCO3 dissolution/precipitation processes, and thus inorganic carbon and coastal carbonate cycling in the CLLMM system. Finally, this coupled δ88/86Sr and 87Sr/86Sr approach can be potentially applied to fossil carbonate archives to reconstruct paleo-hydrology and salinity changes in the CLLMM and/or other carbonate-producing coastal systems.

Unravelling the hydrological effects on spatiotemporal variability of water chemistry in mountainous rivers from Southwest China

AbstractUnderstanding the effects of hydrological processes on solute dynamics is critical to interpret biogeochemical processes. Water chemistry and isotopic compositions of surface water (δ18Ow and δDw) were investigated in rivers from Southwest China to study the effects of hydrological variability on biogeochemical processes. The inverse relationship between deuterium excess (d‐excess) and δ18Ow could be ascribed to non‐equilibrium fractionation processes, and the slope of the Local River Water Line was much lower than the Local Meteoric Water Line, suggesting the post‐precipitation evaporation pattern. The evaporation fraction (1–f) was estimated by the d‐excess method, varying from 0.01 to 0.18. (1–f), was a function of water temperature and drainage mean elevation, indicating that evaporation easily occurs at high temperatures in low‐elevation regions. The hydrological processes co‐varied with solute dynamics in the river network, and fluid transit time and temperature were likely responsible for the co‐variations. Also, we found that hydrological processes played an important role in solute dynamics through shifting the geochemical processes (e.g., enrichment, water‐rock reaction, photosynthesis, and secondary mineral precipitation). This study highlights that biogeochemical processes co‐vary with hydrological processes, and we suggest that investigating hydrological processes can help to understand biogeochemical processes.

Variability in Environmental Conditions Strongly Impacts Ostracod Assemblages of Lowland Springs in a Heavily Anthropized Area

The Po river plain (Northern Italy) hosts artificial, lowland springs locally known as fontanili, which provide important ecosystem services in an area dominated by intensive agricultural activities. Here we present a study carried out in 50 springs. Each spring was visited once from October 2015 to January 2016. The sampled sites were selected to include springs studied in 2001 and 2004, to evaluate changes in water quality and ostracod assemblages that possibly occurred over a period of 10–15 years, and explore the relationships between ostracod community composition and water physical and chemical variables. Our results showed a decrease in the chemical water quality especially, in springs south of the Po river, evidenced by high nitrate levels. Most of the studied springs showed a relevant decrease in dissolved reactive silica, probably related to recent transformations of either agricultural practices or crop typology. Ostracods were mostly represented by common and tolerant species, and communities were characterized by low alpha diversity and high species turnover. Water temperature and mineralization level were the most influential variables in structuring the ostracod communities. We stress the need to implement conservation and restoration measures for these threatened ecosystems, to regain their role as ecosystem services providers.

Assessing the impact of land use and liming on stream quality, diatom assemblages and juvenile salmon in Wales, United Kingdom

Many freshwaters in base-poor upland areas of Britain continue to be affected by acidification as a result of deposition of air pollutants, and agricultural and forestry practices. The effects of land use and annual liming on stream chemistry, diatoms and salmon populations were investigated over eight years in the upper catchment of the River Wye, Wales, United Kingdom. Variations in water chemistry, diatom species composition and diversity, and in the index Diatom Acidification Metric (DAM) were compared between different types of land cover and flow conditions, and before and after applications of lime. Two methods of liming, hydrological source (catchment) liming and sand liming (in-stream liming), were used to reduce stream acidity. Electrofishing was carried out for several years before and after liming to monitor the recovery of salmon populations.Prior to liming, water chemistry differed between stream sub-catchments with differing land use. ANC, Ca concentrations and pH were lower, and Al concentrations were higher, in areas with conifers and acid grassland than in areas with improved grassland and broadleaf woodland. After liming pH increased, but the effects differed between sites and were dependent upon pH levels before any liming began, flow conditions, and the method of liming. An increase in pH during high flows was evident at many sites where acid episodes had occurred prior to liming.Diatom species richness and diversity were low, many sites supporting only 10–15 species. Correlations of richness and diversity with water chemistry were not significant but there was a tendency for low pH sites to support very few species. Species richness was highest in areas adjoining broadleaf woodland and improved grassland, and lowest in areas adjoining conifer plantations.Diatom species composition changed after liming and depended on the type of dominant land cover in the catchment areas and the method of liming. Species tolerant of low pH, in particular Eunotia exigua, became less abundant and were replaced by acid-sensitive species, predominantly Achnanthidium minutissimum. DAM index values and ecological quality ratios (EQR), which were both lower in conifer and acid grassland areas before liming than elsewhere, improved after liming and in many areas the ecological status class of limed streams became good or high. The change to diatom assemblages with predominantly acid-sensitive species after liming correlated with increasing numbers of juvenile salmon and their expansion upstream to sites that had lacked fish prior to liming.

The Structure and Composition of Puerto Rico's Urban Mangroves.

This study characterizes the structure and composition of mangrove forests across urban gradients in Puerto Rico. It then uses a suite of hydrologic, water chemistry, and land cover variables to test for the relative importance of urban intensity alongside flooding and water chemistry in explaining observed variability in forest structure and composition. Three separate statistical tests suggest a significant but limited influence of urbanness on forest composition and structure. In the most urban sites, the diameters of the largest trees were 27% larger, but all structural measurements were best explained by surface water chemistry, primarily nitrogen concentrations. Concentrations of ammonium and total Kjeldahl nitrogen best explained stem density, tree girth and canopy height. The most urban forests also contained 5.0 more species per hectare, on average, than the least urban forests, and simple regression suggests that urban metrics were the most powerful predictors of forest composition. The most urban forests were more dominated by Laguncularia racemosa, while both Avicennia germinans and Rhizophora mangle were found to be less abundant in the most urban sites, a trend that may be linked to the influence of precipitation and tidal connectivity on porewater salinity across the urban gradient. In multiple regression, no statistical difference was detected in the importance of surrounding land cover, flooding, or water quality in explaining the variance in either composition or structural metrics. This suggests that while a given forest metric may be strongly linked to either land cover, water quality, or flooding, all three are likely important and should be considered when characterizing these forests. With more human dependents in urban areas, the provisioning of important ecosystem services may be influenced by land use variables in addition to the more commonly measured metrics of water chemistry and flooding.

Factors Influencing the Occupancy and Abundance of Streamside Salamander (Ambystoma barbouri) in Kentucky Streams

For many amphibian species of conservation concern, our understanding of drivers of distribution and abundance are based on data collected at only a few localities. Thus, landscape-scale efforts are needed to better inform management and species conservation. The Streamside Salamander (Ambystoma barbouri) is a global conservation priority because of its restricted geographic distribution and presumed sensitivity to forest loss, yet landscape-scale studies have not occurred. We surveyed a 16-county area in Kentucky (USA) and examined the influence of catchment (forest, agriculture, and urban) and local-scale (water chemistry and sunfish presence) variables on A. barbouri occupancy and abundance. We sampled 80 streams across different land cover types (i.e., 30 agriculture, 34 forested, and 16 urban) over 2 yrs (2017–2018). Within these streams, we identified 56 new localities. Estimated mean occupancy (Ψ = 0.91; credible interval [CI] = 0.76–0.99) was high. Streams with the highest estimated abundances were those without sunfish and containing >50% forested or agricultural land cover within their catchments; urban streams had the lowest estimated abundances. At sites where we did not detect sunfish, there were an estimated 35.25 (95% CI = 32.04–38.67) A. barbouri individuals per 10 m in forested sites, 22.47 (95% CI = 19.86–25.14) in agricultural sites, and 0.66 (95% CI = 0.14–1.59) in urban sites. Water chemistry varied across site types; however, only maximum sodium (β = –0.51, 95% CI = –0.58 to –0.43) was associated with A. barbouri abundance. If managing this species becomes necessary, minimizing urban development within low-order stream catchments should be a priority.

Current distributions and future climate‐driven changes in diatoms, insects and fish in U.S. streams

AbstractAimBiodiversity on Earth is threatened by climate change. Despite the vulnerability of freshwater habitats to human impacts, most climate change projections have focused on terrestrial systems. Here, we examined how the current distributions and biodiversity of stream taxa might change under mitigated, stabilizing and increasing greenhouse gas emissions.LocationConterminous USA.Time periodPresent day to 2070.Major taxa studiedStream diatoms, insects and fish.MethodsWe developed species distribution models for 336 freshwater taxa from 1,227 distinct stream localities using water chemistry, watershed and climatic variables. Models based only on climate were used to project changes in the distributions and biodiversity of cold‐ versus warm‐water taxa under representative concentration pathways (RCPs) ranging from 2.6 to 8.5 W/m2.ResultsIn all three organismal groups, climate emerged as the strongest predictor of species distributions, providing comparable explanatory power to water chemistry and watershed variables combined. The RCP‐based projections suggested a widespread expansion of warm‐water taxa, outpacing the decline of cold‐water taxa. Consequently, overall species richness would increase, but beta diversity would decrease drastically with the severity of climate change. A closer look at individual taxa and functional guilds revealed that vulnerable cold‐water taxa included: (a) diatom guilds forming the base and bulk of the biofilm; (b) environmentally sensitive insects, characteristic of unimpacted streams; and (c) ecologically and recreationally important salmonids, which were forecast to diminish dramatically in source habitats. Warm‐water fish projected to increase their distributions include bait bucket release minnows and dominant predators.Main conclusionsOur results suggest potentially devastating impacts of climate change on stream ecosystems, with the restructuring of diatom, insect and fish communities, diminished distributions of functionally important taxa and widespread expansion of warm‐water taxa, giving rise to biotic homogenization. Given that the magnitude of these biotic shifts depends on the severity of climate change, appropriate current policy decisions are necessary to preserve freshwater ecosystems.

Fatty acids reveal aquaculture and drought effects on a large tropical reservoir

Fatty acids (FAs) and their metrics have been used to detect and assess the impacts of urbanization and agriculture on aquatic ecosystems. Here, we investigated whether seston FAs are also useful to characterize and understand early-stage aquaculture impacts in a large tropical reservoir (Furnas Reservoir, SE Brazil). We tested the hypothesis that single FAs, as well as selected FA metrics in the seston fraction, are efficient markers of net-cage fish farming effects. In general, fish farming had only minor effects on standard water chemical variables, mainly small increases in ammonium, nitrate, and dissolved organic nitrogen concentrations. By increasing concentrations of several polyunsaturated FAs, early-stage fish farming improved sestonic food quality in the more oligotrophic branch of the reservoir under drought conditions. However, in general, increases in concentrations of bacterial FAs, due to fish farming, suggested organic matter (OM) subsidies from non-ingested and non-assimilated fish feed. In the more eutrophic reservoir branch, seston FA profiles suggested that fish farming caused an increase of low-quality food resources, such as cyanobacteria. Thus, background impact levels may determine the biochemical responses of tropical reservoirs to fish farming. Higher contributions of potentially sewage-derived and bacterial FAs during drought conditions, especially at reference sites of the more oligotrophic branch, suggested that drought shifted OM inputs towards anthropogenic sources, thereby overwriting land-use related differences between reservoir branches and homogenizing their environmental conditions. In conclusion, FA variables were useful to evaluate and understand environmental conditions, as well as the effects of early-stage fish farming and drought, and should be considered in impact assessments in tropical lentic ecosystems.

Bioavailability and phytotoxicity of rare earth metals to Triticum aestivum under various exposure scenarios

It is a daunting challenge to predict toxicity and accumulation of rare earth metals (REMs) in different exposure scenarios (e.g., varying water chemistry and metal combinations). Herein, we investigated the toxicity and uptake of La and Ce in the presence of various levels of Ca, Mg, Na, K, and at different pH values, as well as the combined effects of La and Ce in wheat Triticum aestivum. Major cations (Ca2+ and Mg2+) significantly mitigated the toxicity and accumulation of La3+/Ce3+. Toxicity and uptake of La, Ce, and La–Ce mixtures could be well quantified by the multi-metal biotic ligand model (BLM) and by the Langmuir-type uptake model with the consideration of the competitive effects of Ca2+ and Mg2+, with more than 85.1% of variations explained. The derived binding constants of Ca, Mg, La, and Ce to wheat root were respectively 3.87, 3.59, 6.97, and 6.48 on the basis of toxicity data, and 3.23, 2.84, 6.07, and 5.27 on the basis of uptake data. The use of the alternative WHAM-Ftox approach, requiring fewer model parameters than the BLM but with similar Akaike information criterion (AIC) values, successfully predicted the toxicity and accumulation of La/Ce as well as toxicity of La–Ce mixtures, with at least 76.4% of variations explained. However, caution should be taken when using this approach to explain the uptake of La–Ce mixtures. Our results provided promising tools for delineating REMs toxicity/uptake in the presence of other toxicity-modifying factors or in mixture scenarios.

A database of chlorophyll and water chemistry in freshwater lakes

Measures of chlorophyll represent the algal biomass in freshwater lakes that is often used by managers as a proxy for water quality and lake productivity. However, chlorophyll concentrations in lakes are dependent on many interacting factors, including nutrient inputs, mixing regime, lake depth, climate, and anthropogenic activities within the watershed. Therefore, integrating a broad scale dataset of lake physical, chemical, and biological characteristics can help elucidate the response of freshwater ecosystems to global change. We synthesized a database of measured chlorophyll a (chla) values, associated water chemistry variables, and lake morphometric characteristics for 11,959 freshwater lakes distributed across 72 countries. Data were collected based on a systematic review examining 3322 published manuscripts that measured lake chla, and we supplemented these data with online repositories such as The Knowledge Network for Biocomplexity, Dryad, and Pangaea. This publicly available database can be used to improve our understanding of how chlorophyll levels respond to global environmental change and provide baseline comparisons for environmental managers responsible for maintaining water quality in lakes.

Conservation implications of fish-habitat relationships in channelized agricultural headwater streams.

Channelized agricultural headwater streams are common throughout agricultural watersheds in the midwestern United States. Understanding fish-habitat relationships within these streams will provide information that can assist with developing conservation and restoration strategies for these degraded streams. From spring 2006 to fall 2010, we collected fishes and measured riparian habitat, instream habitat, and water chemistry variables from seven sites in Cedar Creek, Indiana, and 14 sites in Upper Big Walnut Creek, Ohio. We found that fish community structure was more strongly correlated with instream habitat than riparian habitat or water chemistry in both watersheds. We also observed interrelationships among instream habitat, watershed size, and fish communities within both watersheds that suggest that the hydrological changes that occur with increasing watershed size are the underlying factor for fish community changes that occur with increasing watershed size. Our results suggest that conservation and restoration efforts within channelized agricultural headwater streams in the midwestern United States, where nutrients and herbicide concentrations are low, need to address physical habitat degradation to positively influence fish community structure.

Optimization of disinfectant dosage for simultaneous control of lead and disinfection-byproducts in water distribution networks

Drinking water utilities are increasingly facing the challenges of maintaining water quality, and simultaneously complying with conflicting regulatory standards. One such challenge is the dosage of chlorine-based disinfectants which is typically regulated to prevent microbial growth in the water distribution systems, while limiting disinfection by-products (DBPs). On the other hand, chlorine residuals also influence the dissolution of lead into drinking water from corrosion scales in the pipe internals, as has been shown by previous studies. Hence, it is important to consider water lead levels (WLLs) while determining the appropriate chlorine dosage. This study proposes a multi-objective optimization framework to understand and balance the trade-offs between (i) minimizing total disinfectant dosage to reduce DBPs formation potential, and (ii) maximizing the volume of safe drinking water supply with respect to both WLLs and residual free chlorine concentrations. The approach comprises of the development of a dynamic simulation-optimization framework to account for the impact of spatial and temporal variations of network hydraulics and water chemistry on WLLs and residual free chlorine. The framework couples dynamic multi-species water quality simulations (pH, residual free chlorine, dissolved inorganic carbon, and orthophosphate concentration) with a multi-objective genetic optimization algorithm in an integrated MATLAB-EPANET-MSX platform. The application of the optimization formulation is demonstrated on a real-world distribution network case study. The resulting optimal solution set on pareto-plots are discussed for sensitivity of the trade-offs between the two objective functions, under various water chemistry conditions that have been suggested in earlier studies for minimizing lead release from plattnerite (PbO2) corrosion scales in lead service lines. The resulting optimal disinfectant dosage schedule, for pumping and booster station nodes in each case, provided insights on maintaining disinfectant residuals throughout the distribution system so as to prevent microbial growth as well as lead contamination events while limiting DBPs formation. Further, environmental implications related to the use of the proposed framework are also discussed.

Insight into the mechanisms of denitrification and sulfate reduction coexistence in cascade reservoirs of the Jialing River: Evidence from a multi-isotope approach

The coexistence of denitrification and bacterial sulfate reduction (BSR) processes is commonly observed in natural water systems. However, its formation mechanism remains unclear at a basin scale due to the difficulty of precise identification of these processes. To address this issue, we investigated the spatial-temporal variations in water chemistry and isotopic compositions (e.g., δ13CDIC, δ15NNO3, δ18ONO3, δ34SSO4, and δ18OSO4) in cascade reservoirs (artificial dam lakes) of the Jialing River, SW China in 2016. The results showed that the denitrification and BSR processes coexisted in the studied reservoirs, which was supported by the positive correlation between δ15NNO3 and δ18ONO3 and between δ34SSO4 and δ18OSO4, and by the decreasing concentrations of NO3− and SO42−. Moreover, covariation of Δ13CDIC, Δ15NNO3, and Δ34SSO4 indicated the dominance of heterotrophic denitrification (HD) in the reservoir waters along with the occurrence of bacterial sulfide oxidation (BSO). In addition to SO42− and NO3−, the coexistence of HD and BSR processes were also controlled by the dissolved organic carbon (DOC) in winter and dissolved oxygen (DO) contents in other seasons. Overall, the cumulative effect of cascade reservoirs caused δ15NNO3 and δ34SSO4 to display an upward trend from upstream to downstream in the Jialing River, while δ13CDIC showed an opposite downward trend, which implying that cascade reservoirs may be in favor of the coexistence of the HD and BSR processes. This study therefore concludes that the multi-isotope approach could be a useful technique to ascertain the coexistence mechanism of HD and BSR processes in reservoir water systems.